The present invention relates to a molding machine for cores of molding sand, completely automatic and structured so as to allow to obtain cores, even small and therefore fragile and delicate ones, free from defects and with minimum production rejects.
As is known, molding machines for cores of molding sand employ a head for the violent injection, by means of compressed air, of the sand (usually sand and various additives) within dies or core boxes placed at the base of the head itself, which dies are composed of two semi-dies, divisible one from the other along a horizontal plane and, in some instances, along a vertical plane.
In the most recent machines, the head is provided with a cylindrical injection chamber, which is arranged vertically and is associated with a compressed air tank; furthermore, it is mounted movable horizontally, with respect to the core boxes, from a working position to a molding sand loading position and, possibly, also to a washing and maintenance position. The operating phases consist of feeding the sand into the cylindrical chamber up to a preset level, then feeding compressed air into the chamber itself so as to launch it, practically shoot it, within the core box associated with the base of the chamber, interrupting the air feed and separating and moving the head away from the molds.
Then a suitable treatment gas is fed in the core box, substantially for curing, then the dies are opened and moved apart; finally, extraction is performed, by various expulsion systems, of the core from one of the dies to which it has been left hanging, and the removal thereof is carried out on a conveyor belt or the like.
Machines of the prior art have, practically, several disadvantages, mostly due to the system for feeding compressed air into the chamber, for its discharge to the outside after packing the sand in the core box and to the system used for divaricating the dies and for unloading the molded core. Indeed, generally, the air fed from above generates turbulent motions and air bubbles which cause an insufficient and irregular distribution of the density of the sand which has been fed, as well as irregularities in the compactness and uniformity of the molded cores, with a consequent dangerous fragility and a high number of rejects. Similarly, the methods adopted for raising both dies in order to matchingly close them against each other and against the base of the injection chamber imply high constructive complexities, while the extraction of the molded core from the cavity (downwardly directed) of the upper die and its free fall onto a conveyor belt often entail irreparable damage to the core themselves, especially to those having small dimensions or being very complex.